Origins of Portal Hypertension in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a major cause of liver disease worldwide. We estimated the global prevalence, incidence, progression, and outcomes of NAFLD and nonalcoholic steatohepatitis (NASH). PubMed/MEDLINE were searched from 1989 to 2015 for terms involving epidemiology and progression of NAFLD. Exclusions included selected groups (studies that exclusively enrolled morbidly obese or diabetics or pediatric) and no data on alcohol consumption or other liver diseases. Incidence of hepatocellular carcinoma (HCC), cirrhosis, overall mortality, and liver-related mortality were determined. NASH required histological diagnosis. All studies were reviewed by three independent investigators. Analysis was stratified by region, diagnostic technique, biopsy indication, and study population. We used random-effects models to provide point estimates (95% confidence interval [CI]) of prevalence, incidence, mortality and incidence rate ratios, and metaregression with subgroup analysis to account for heterogeneity. Of 729 studies, 86 were included with a sample size of 8,515,431 from 22 countries. Global prevalence of NAFLD is 25.24% (95% CI: 22.10-28.65) with highest prevalence in the Middle East and South America and lowest in Africa. Metabolic comorbidities associated with NAFLD included obesity (51.34%; 95% CI: 41.38-61.20), type 2 diabetes (22.51%; 95% CI: 17.92-27.89), hyperlipidemia (69.16%; 95% CI: 49.91-83.46%), hypertension (39.34%; 95% CI: 33.15-45.88), and metabolic syndrome (42.54%; 95% CI: 30.06-56.05). Fibrosis progression proportion, and mean annual rate of progression in NASH were 40.76% (95% CI: 34.69-47.13) and 0.09 (95% CI: 0.06-0.12). HCC incidence among NAFLD patients was 0.44 per 1,000 person-years (range, 0.29-0.66). Liver-specific mortality and overall mortality among NAFLD and NASH were 0.77 per 1,000 (range, 0.33-1.77) and 11.77 per 1,000 person-years (range, 7.10-19.53) and 15.44 per 1,000 (range, 11.72-20.34) and 25.56 per 1,000 person-years (range, 6.29-103.80). Incidence risk ratios for liver-specific and overall mortality for NAFLD were 1.94 (range, 1.28-2.92) and 1.05 (range, 0.70-1.56).

Liver fibrosis is the most important predictor of mortality in nonalcoholic fatty liver disease (NAFLD). Quantitative risk of mortality by fibrosis stage has not been systematically evaluated. We aimed to quantify the fibrosis stage-specific risk of all-cause and liver-related mortality in NAFLD. Through a systematic review and meta-analysis, we identified five adult NAFLD cohort studies reporting fibrosis stage-specific mortality (0-4). Using fibrosis stage 0 as a reference population, fibrosis stage-specific mortality rate ratios (MRRs) with 95% confidence intervals (CIs) for all-cause and liver-related mortality were estimated. The study is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Included were 1,495 NAFLD patients with 17,452 patient years of follow-up. Compared to NAFLD patients with no fibrosis (stage 0), NAFLD patients with fibrosis were at an increased risk for all-cause mortality, and this risk increased with increases in the stage of fibrosis: stage 1, MRR = 1.58 (95% CI 1.19-2.11); stage 2, MRR = 2.52 (95% CI 1.85-3.42); stage 3, MRR = 3.48 (95% CI 2.51-4.83); and stage 4, MRR = 6.40 (95% CI 4.11-9.95). The results were more pronounced as the risk of liver-related mortality increased exponentially with each increase in the stage of fibrosis: stage 1, MRR = 1.41 (95% CI 0.17-11.95); stage 2, MRR = 9.57 (95% CI 1.67-54.93); stage 3, MRR = 16.69 (95% CI 2.92-95.36); and stage 4, MRR = 42.30 (95% CI 3.51-510.34). Limitations of the study include an inability to adjust for comorbid conditions or demographics known to impact fibrosis progression in NAFLD and the inclusion of patients with simple steatosis and nonalcoholic steatohepatitis without fibrosis in the reference comparison group.